The isolation and purification of nucleic acids is a critical first step in many research and diagnostic applications. Purified nucleic acids must be of high quality, such that they can be used in sensitive downstream applications including PCR amplification, detection, sequencing, cloning and hybridization. Obtaining purified DNA or RNA is a complicated task due to the presence of large amounts of contaminating cellular materials, (e.g. proteins and carbohydrates) present in the complex environments in which the nucleic acids are found, including urine, blood, plasma, serum, saliva, feces, milk, tissues, plants, soil, yeast and fungi.
Furthermore, in addition to providing purified nucleic acids for use in downstream applications, it is also important to ensure that total nucleic acids are isolated from a sample. This is particularly important for the isolation of RNA that may be used for studies involving gene expression and gene regulation, as the quantity of a specific RNA within a cell indicates the level of expression of a particular DNA. In recent years, the study of gene expression has increased, with gene activity and nucleic acids obtained from biological samples being used to diagnose infections or diseases including cancer, and to monitor the effects of administered drugs, among other applications. Information relating to the presence and quantity of a specific RNA is critical in studying gene expression; therefore it is critical that the method of nucleic acid isolation being employed does not favour the isolation of certain sizes of RNA molecules.
Many different methods for the isolation and purification of nucleic acids have been developed over the years. Traditional methods for the isolation of nucleic acids involve the use of phenol or an organic solvent mixture containing phenol and chloroform to extract cellular materials followed by precipitation of the nucleic acids with alcohol. These traditional methods are problematic as they are time consuming (e.g. require multiple extraction steps), require the use of toxic chemicals and often provide low yields of nucleic acid. Further, the purified nucleic acids can be contaminated with the organic solvents or alcohol, both of which interfere with downstream applications.
Newer methods for the purification of nucleic acids are based on solid phase purification. With solid phase purification, the nucleic acid of interest is bound to a solid support, while impurities such as proteins and other non-target nucleic acids are washed away. The purified nucleic acid of interest is then eluted from the solid support. The first solid phase purification methods were based on the use of silica. Silica materials such as glass particles, glass powder, silica particles, glass microfibers, and diatomaceous earth have been used in combination with aqueous solutions of chaotropic salts to isolate DNA and RNA. Methods for the purification of nucleic acids using other types of support materials have also been developed, including the use of silicon carbide (SiC).